1. Field of the Invention
The present invention concerns a new process for the chemical synthesis of polysilsesquioxanes giving compounds with high molecular mass and reduced polydispersivity and increased stability over time. These improvements enable the performance characteristics of the polysilsesquioxanes to be used in applications in microelectronics, in using them to make a negative resin with very high sensitivity and high contrast for insolation by electrons or X-rays, or more generally for use in integrated optics.
The use of siliceous polymers in microelectronics has developed in recent years because such materials, more especially polysilsesquioxanes, are filmogenic and have many uses in microelectronics.
2. Description of the Prior Art
The first modes of synthesis of polysilsesquioxanes have drawn inspiration from the process described by G. H. WAGNER et al. in Ind. and Eng. Chem., vol. 45, No. 2 (1953), pages 367-374. According to this process, the compound RSiCl.sub.3 is hydrolyzed (R may be an alkyl radical, for example CH.sub.3 or C.sub.2 H.sub.5, or an aryl radical, for example C.sub.6 H.sub.5, or allyl radicals, the most valuable of them from the viewpoint of the applications being the vinyl radical CH.sub.2 =CH). This hydrolysis is done in an ether at low temperature (0.degree. to 5.degree. C.) with a great excess of water. Then, the organic phase is washed abundantly and it is treated to remove the residues of hydrochloric acid while, at the same time, promoting the oligomerization of the product. The etherified phase is then dried, and an oily low-mass oligomer is obtained.
An appreciable improvement in this process has been described in the patent FR 2 144 024 which teaches that, by the optimizing of a quantity of ammonia added, it is possible to achieve a condensation of the products of hydrolysis and to obtain a polymer with a mass of about 1300 having about 2% of residual OH groups. However, this process has the drawback of excessive dispersivity and a relatively low mass as well as an appreciable aging of the polymer due to the presence of the OH groups.
Other patent applications have been filed with a view to making improvements in the above-mentioned processes.
JP 62. 283 128 describes the synthesis of polyallylsilsesquioxane (in this case, R is the group CH.sub.2 CH.dbd.CH.sub.2) terminated by hydroxyl radicals. However, the presence of these hydroxyl radicals means that the compound obtained has little stability under temperature.
EP 255 303 describes a process for the synthesis of the copolymer EQU (CH.sub.2 .dbd.CHCH.sub.2 SiO.sub.3/2).sub.m --(ClCH.sub.2 SiO.sub.3/2).sub.n
where m varies between 0 and 100 and m+n=100. The authors use the above-mentioned Wagner process but in complementing it with a subsequent reprocessing of the product obtained. This is a second polymerization done in a ketonic solvent in the presence of a base. This process is known to achieve an effective increase in the masses of the polysiloxanes but is not enough to reduce the polydispersivity to below 1.5.
Owing to their low molecular mass, their high polydispersivity and the presence of non-stabilized terminal groupings, the materials obtained by these various processes have low performance values in X-ray or electron microlithography.